Joint, synovial fluid and cartilage

Question 1

What is a fibrous joint?

Answer 1

• Composed of collagen fibres and fibrous connective tissue
• The fibers have very high tensile strength
• Not much movement

Question 2

Give examles of fibrous joints

Answer 2

□ Periodontal ligament
□ Cranial structures
□ Interosseous membranes
® Forearm and leg

Question 3

What is a cartilagenous joint?

Answer 3

• A bit more mobile than the fibrous joints but not that mobile
• Primary cartilaginous (Synchondrosis)- only hyaline cartilage
  □ Growth plate (growing long bones)
• Secondary cartilaginous (symphysis)- hyaline and fibrocartilage
  □ Intervertebral disks

Question 4

What are the common features of synovial joints?

Answer 4

□ Synovial cavity (fluid-filled)
□ Articular cartilage
□ Fibrous capsule 
□ Synovial membrane 
□ Synovial fluid

Question 5

Synovial joints may also contain… (that are not common features)

Answer 5

□ Articular disks
□ Ligaments
□ Bursae
® Fluid filled pillows that reduce friction around the joints

Question 6

What are the different types of synoial joints (give an examle for each)?

Answer 6

• Synovial plane: Facet joints
• Synovial hinge: elbow joint
• Pivot joint: Radial ulnar joint
• Synovial condylar (ellipsoid): the radiocarpal joint
• Synovial saddle: between the traezium carale bone and the first metacaral bone
• Synovial ball and socket: shoulder joint

Question 7

How do joints maintain stability?

Answer 7

○ Shape of articulating surfaces
○ Capsule and ligaments
○ Muscles

Question 8

Describe the chondrocytes in the superficial/ tangential layer of articular cartilage

Answer 8

□ Flattened

□ Produces collagen and glycoproteins (e.g. lubricin)

Question 9

Describe the chondrocytes in the

transitional layer of articular cartilage

Answer 9

□ Round

□ Produces proteoglycans such as aggrecan (which can bind water and keeps water in the articular cartilage)

Question 10

Describe the change in collagen orientation in articular carilage

Answer 10

• Parallel in the superficial layer
• Oblique fibers in the transitional layer
• Vertical fibers in the deep layer

Question 11

What percentage of young and healthy articular cartilage is water and why is this?

Answer 11

• > 75%
• Water is incompressible
• This allows the tissue to be protected from being compressed

Question 12

What is the average thickness of articular cartilage in joints and why might it vary deending on the joint?

Answer 12

• 2-3mm
• It depends on the forces acting on the joint
• if it is not weight bearing then the joint doesn’t need as thick articular cartilage
• If when doing certain things the forces acting on the joint are very strong then the joint needs a thicker articular cartilage

Question 13

What are glycoproteins?

Answer 13

• e.g. lubricin
• Proteins to which oligosaccharide chains are attached
• More a protein than a carbohydrate
• A very good lubricator

Question 14

What are proteoglycans?

Answer 14

• e.g. aggrecan
• Proteins that are heavily glycosylated (a protein core to which one or more GAGs attached)
• Tend to be more carbohydrate than protein

Question 15

What are glycosaminoglycans (GAGs)?

Answer 15

• e.g. hyaluronic acid
• Long unbranched polysaccharides, which are highly polar and thus attract water
• Makes the synovial fluid a bit more viscus making it a better lubricator
• It is part of molecules such as aggrecans

Question 16

What are the properties of cartilage? (3 A’s)

Answer 16

○ Avascular
○ Aneural
○ Alymphatic

Question 17

Where is synovial fluid produced?

Answer 17

○ Synovial fluid produced by synovial membrane (synovium)
- Synoviocytes producing the fluid
□ Type A
® Look like macrophages
® Remove debris
® Contribute to synovial fluid production
□ Type B
® Fibroblast like
® Main producer of synovial fluid

Question 18

Describe synovial fluid

Answer 18

○ Viscous fluid
○ Hyaluronic acid & lubricin
○ Fluid component (from blood plasma)
○ Small volumes (knee joint:   ̴0.5 ml )
○ Rapid turnover (  ̴2 hours)

Question 19

What is the function of synovial fluid?

Answer 19

• Nutrition of cartilage (articular c., menisci/discs)
• Removal of waste products
• Lubrication → less friction → less wear
  □ Boundary
  ® Glycoproteins such as lubricin bind to receptors on articular surfaces to form a thin film
  □ Hydrodynamic (like aquaplaning)
  ® Surfaces kept apart by liquid pressure
  ® Viscosity changes with load and velocity of movement
  □ Weeping
  ® Fluid that is present in the cartilage is squeezed out into the synovial cavity to increase fluid volume
  ® When you have high pressure acting on the joint you get weeping lubrication

Question 20

What are bursae?

Answer 20

○ Made up of synovial membrane
○ Fluid-filled
○ In areas with a high level of friction
○ Reduced friction

Question 21

What happens to the joints when aging?

Answer 21

○ Viscosity of synovial fluid increases
- Slower joint movements
- Reduced lubrication
○ Water content of cartilage decreases
- Reduced shock absorption due to the loss of the incompressible water
- Higher risk of damage
- Less protection of articular surfaces & increased risk of damage
○ Osteoarthritis
- Narrow disk
- Bone spur (osteophytes)
- Uncontrolled additional bone growth around the edges